Insulin therapy is characterized by a high need for keeping the insulin drug release within very strict levels as the therapeutic window is narrow, and the adverse effects of hyperinsulinemia can potentially be life threatening. Numerous insulin preparations have been commercialized, with different action profiles to suit specific needs of the diabetic population. Fast acting insulin analogs are administered just before meals, in order to control the peak in plasma glucose following food ingestion, whereas long acting insulin analogs are typically given once or twice a day to provide a steady basal insulin level.
Recent developments have also included oral insulin and inhaled insulin. However, because insulin is a protein, when taken orally it is easily digested by the stomach and gastrointestinal system. Alternatively, inhalable insulin delivered through an inhaler into the lungs was commercially available for a limited period (Exubera®, Pfizer discontinued in 2007). This formulation provided insulin for a period of hours, still requiring patients to continue injecting a long-acting basal insulin. Further disadvantages of the inhalable insulin included manufacturing difficulties resulting in a cost-prohibitive delivery system. As a result, all commercially available insulin formulations must be administered either by subcutaneous or intravenous injection.
The plasma profile of the various available insulins are characterized by having different plasma profiles. Said plasma profiles can be described by having a maximum and a minimum plasma concentration which is dependent on the formulation and type of insulin used. It is of high importance to obtain a plasma profile which is as reproducible from patient to patient and within patients in order to be able to predict the plasma glucose lowering effect of the administered insulin. Additionally, in the case of multiple administrations of basal insulin, it is desirable to have as little difference between the maximum plasma concentration and the minimum plasma concentration as possible. This will lead to a more constant plasma concentration of insulin, and therefore a more uniform glucose lowering effect over the entire dosing interval.
Current standard basal insulin therapy consists of daily or twice daily administrations of long acting basal insulins such as NPH insulin, insulin glargine or insulin detemir. Though development of newer insulin analogs has aimed to reduced the variability of insulinotropic effects, the glucose lowering effect of these long acting formulations are still characterized by large inter- and intra-subject variations as described by Heise et al. (Diabetes, 2004 (53), 1614-1620). In this study insulin detemir displayed the least pharmacokinetic variation, with a coefficient of variation of 15 as compared to CV of NPH insulin and insulin glargine of 26 and 34, respectively. This rather large variability is a major obstacle to obtaining optimal glucose control, as it is difficult to predict the exposure to the insulin molecules.
The same study investigated the pharmacodynamic variation as assessed by glucose infusion rates (GIR). This evaluation also demonstrated that insulin detemir had lower within-subject variability than both NPH insulin and insulin glargine with respect to the pharmacodynamic marker GIR. Furthermore, this study demonstrated that the insulin effect on glucose infusion rates did not last throughout the full dosing period of 24 hours, clearly demonstrating the need for a long acting insulin, that offer full glucose lowering action for the full duration between doses. To circumvent the problem of current daily basal insulins not lasting a full 24 hours, some patients split their basal insulin dosage into two daily injections, in order to obtain better glucose control throughout the day.
Therefore, there is a clear need for novel long acting preparations of insulin, that continuously release insulin throughout the entire period between administrations.
In addition, even if patients can manage their blood glucose with daily injections of basal insulin, initiation of insulin therapy meets reluctance due to the daily injection regime. This is undesirable, as the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) recognize insulin as first line treatment after oral metformin as offering the best treatment outcome. (D M Nathan et al., Diabetologica (2008) 51:8-11).
If the injection frequency of insulin treatment could be reduced, it is likely that the psychological barrier to initiation of insulin therapy would be reduced, hence allowing patients to start insulin therapy at an earlier stage, greatly improving their health status.
A challenge in developing long-acting basal insulin formulations lies in the narrow therapeutic range for insulin, and large peak-to-trough variations in insulin pharmacokinetics as well as burst effects should be avoided under all circumstances.
Several approaches to reducing the frequency of administration, while still retaining the insulin release within narrow limits have been proposed, but have failed to extend the duration of glucose lowering effects beyond a couple of days, while still being characterized by having a small ratio between the maximum plasma concentration and the minimum plasma concentration.
WO 06003014 describes a hydrogel capable of releasing insulin with the possibility of reduced dosing frequency as compared to standard daily basal insulin injections. However, the insulin is released at a rate too fast for ensuring strict insulinotropic control for periods extending 2 days. In fact the insulin is released with a half life of approximately 30 hours, meaning that the prodrug must be administered at least every 30 hours in order for the peak to trough ratio to be below 2 at steady state.
The concept of preparing a reversible polymer conjugate of insulin has been explored by Shechter et al. and described in scientific articles and patent applications (e.g. (European Journal of Pharmaceutics and Biopharmaceutics 2008(70), 19-28) and WO 2004/089280). The insulin is conjugated to a 40 kDa PEG polymer through a 9-hydroxymethyl-7-(amino-3-maleimidopropionate)-fluorene-N-hydroxysucinimide spacer molecule. Hydrolysis of said spacer molecule releases insulin with a half life of approximately 30 hours, meaning that the prodrug must be administered at least every 30 hours in order for the peak to trough ratio to be below 2 at steady state.
Other attempts of reducing the insulin dosing frequency have been made. Hinds et al (Journal of Controlled Release, 2005 (104), 447-460) describe a method of producing a once weekly insulin, by first permanently PEGylating the insulin molecule and then subsequently microencapsulating the PEGylated insulin in PLGA microparticles. PLGA encapsulation of proteins has been shown to cause side reactions of the polymer esters with peptide or protein amino groups. Lactic acid acylation products have been observed after exposure of the formulations to buffered solutions at neutral pH. (Nat. Biotechnol. 18 (2000) 52-57; Pharm. Res. 11 (1994) 865-868; Pharm. Res. 19 (2002) 175-181).
Specifically for insulin, detrimental effects of polymer formulations have been demonstrated (Pharm. Dev. Technol. 4 (1999) 633-642; Pharm. Dev. Technol. 5 (2000) 1-9).
In the abovementioned case, the insulin has undergone substantial structural modification through permanent modification by a high molecular weight polymer entity as PEGylation of insulin apparently serves to protect the peptide from deterioration in the PLGA polymer formulation.
Unfortunately, such high molecular weight modified insulins may exhibit reduced efficacy by diminished receptor binding and may also exhibit injection site reactions such as lipodystrophy due to the extended presence of high concentrations of the high molecular weight insulin in the subcutaneous tissue. Furthermore, such PEGylated insulins will exhibit a lower distribution volume, which is of particular disadvantage in the treatment of diabetes.
In addition, the pharmacokinetic profile of the released insulin conjugate is characterized by an initial burst-like release immediately following administration, which is followed by a drop in insulin conjugate plasma concentration, followed by an increase in insulin conjugate plasma concentration over the following days. This pharmacokinetic profile is typical of microencapsulated drug formulations and can lead to an unpredictable glucose response in subjects treated with such formulation.
Therefore the challenge remains to develop long-acting insulin without compromising the insulin pharmacodynamics effects by permanent attachment of a high molecular weight entity.
The situation is further complicated by the fact that insulin is known to readily undergo side reactions that are related to the presence of three disulfide bridges in the molecule. For instance, insulin may be split into A and B chains by disulfide bond cleavage or dimers or oligomers may be formed due to disulfide interchange reactions. Such disulfide reshuffling is particularly likely, if insulin molecules are forced into close contact in a random way (“Stability of insulin: studies on the physical and chemical stability of insulin in pharmaceutical formulation”, Jens Brange, Springer, 1994). This intrinsic lability of the insulin molecule has significantly hampered progress in long-acting depot development and prevented the use of other polymer formulations where insulin is encapsulated in a way similar to an amorphous precipitate which is well known to give rise to various degradation products arising from extensive disulfide exchange.
The rate of side reactions is further influenced by the concentration of insulin, with the rate being higher when insulin is present in high concentration. It is therefore challenging to formulate high concentration long acting insulin formulations, in which insulin does not undergo undesirable side reactions.
Therefore, there is a clear need for novel long acting preparations of insulin that continuously release structurally intact insulin throughout the entire period between administrations, which at the same time retains a small ratio between the highest and lowest insulin plasma concentration in order to avoid too high or too low insulin concentrations, that can be potentially harmful for a patient.
The insulin requirement for diabetics is highly individual, with the dose depending on several physiological factors, including pancreatic beta cell function, insulin sensitivity, body weight and dietary intake. It is not uncommon for patients to require 40 IU of insulin or more per day. This is equivalent 280 IU/week which corresponds to 12.6 mg human insulin per week. In order to minimize the discomfort for the patient, this should be formulated in a small volume, for example one milliliter. It is therefore an object of the current invention, to provide an insulin formulation, in which the concentration of insulin is at least 10 mg/mL, while still releasing structurally intact insulin and displaying a substantially burstless pharmacokinetic profile. Furthermore, as a consequence, it is an object of the current invention that a single dose of the long acting insulin can be administered as a single injection of the formulation, containing at least 10 mg insulin compound.
US2007/0207210 A1 describes a method of preparing amorphous microparticles of high molecular weight proteins, and in particular antibodies. Insulin is mentioned in an example as being formulated in up to 400 mg/ml according to the disclosure. However, the object of the invention is to provide a formulation with similar pharmacokinetic profile to native protein, hence not to provide a sustained release. US2007/0207210 A1 therefore does not offer a solution to reducing the dosing frequency of insulin.